Tritium is a low energy beta emitter, and while it is not dangerous externally, it is a radiation hazard upon inhalation, ingestion or absorption. Tritium can be produced in nuclear power generation as a by-product of the fission of uranium-235, plutonium-239, and uranium-233 as well as by neutron activation of lithium-6. In heavy water moderated and cooled reactors tritium can be produced when a deuterium nucleus captures a neutron. Though relatively small amounts of tritium are produced via such routes, it readily binds hydroxyl radicals to form tritiated water. As such, tritiated water can build up over time within cooling water as well as within water used in storage pools at nuclear power generating facilities which can lead to environmental contamination. Accidental release of tritiated water from nuclear power generation facilities is understood to be the major source for aqueous release of radioactivity to surface streams and rivers, and the 2011 Japanese earthquake resulted in the release of millions of gallons of tritium-contaminated water from the Fukushima Daiichi nuclear plant. Tritium contamination of groundwater in the vicinity of nuclear power generation facilities has led to public outcry and negative publicity for the nuclear power industry.
Methods that have been developed for the removal of tritium from contaminated water include water distillation, cryogenic distillation, electrolysis, and gas/liquid catalytic exchange. Unfortunately, problems exist with such methods. For instance, water distillation is energy intensive, as the water (H2O) vapor pressure is only 1.056 times of that of tritiated water (HTO). Due to a high reflux ratio of about 30, huge reboiler duty and large column diameter are required. The small separation factor also requires an extreme column height for the hundreds of theoretical plates necessary for the process. Cryogenic distillation has shown promise, but the successful production experience of more recently developed technologies such as the thermal cycling adsorption process (TCAP) exhibit improved performance. Electrolysis has a very good tritium separation factor however it is difficult to stage and is very energy intensive. Catalytic exchange has been combined with electrolysis in a process known as Combined Electrolysis Catalytic Exchange (CECE), which is the leading production-scale process to decontaminate tritiated water. Unfortunately, the process requires a high concentration of tritium in the treatment water and the current capacity is still orders of magnitudes smaller than the need in many facilities.
Effective treatment of tritiated water is technically very challenging due to the large volume and low contaminant concentration of existing tritiated water. For instance, existing storage facilities are more than 90% full and contain hundreds of thousands of tons of contaminated water for treatment. There are simply no current methods or systems that can handle such volume.
What are needed in the art are methods and systems that can separate isotopes such as tritium from contaminated water sources efficiently. High isotope selectivity (or separation factor) and scalable process are important components of the need.